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"WARNING" ARP Head Studs- proven wrong

First off i will say i'am a big fan of ARP products. But i had a engine fail in the weekend that was partly caused by the arp head studs. I found that both camshafts had starved of oil. After pulling the head and checking the oil flow/pressure coming out of the block to the head, i found the problem. The oil feeds up the side of the bolt into a oil galley 1/2 way up the bolt hole and thats how the cams are feed. After checking the hole for the head stud against the toyota factory bolt and then the ARP head stud i found the problem.
the toyota bolt is 8.41mm thick
the ARP head stud is 10.00 thick
and the hole for the head stud is only 10.80mm wide.
So that means there is only a .40mm gap for the oil to flow into the oil gallery. My fix for this is to machine a 3-5mm groove up the bolt hole to the oil gallery.

I hope this article helps someone out as i'am up for 2 new cams and 3 months of porting and about $900 of machine work again. i dont wish that on anyone.

i found that the other day. its a good read. what suprises me is the difference's in his spec's to mine. He has measured the id of the head oil gallery which is 1.86, so i still believe the .4 is just a little to small. I'll get the groove machined and post the pics. i dont wish this shit on anyone else.

Lets clarify this shall we.
Firstly, only the front two cam journals are fed via a dedicated gallery, the others are splash lubricated from being in the valvetrain bath. The gallery feeding the cam journals exits 5.4mm below the machined washer face on the front exhaust side bolt hole.
Secondly, the Toyota head bolts are chamfered NOT so that it aids in oil flow, but rather because that is how they get their accuracy for Torque to Yield ratings. They do it on a lot of their engines, 7Ms, 2JZs etc, all with different chamfered lengths and thicknesses, they even do it on engines which have dedicated oil galleries (i.e. not via the head stud/bolt passage).
Thirdly, if you had assembled the engine correctly, i.e. with the dowels, you wouldnt have this issue.
Fourthly, the oil for that gallery is fed via the head gasket, and as such the oil flow is determined not only by the area around the bolt but also by the head gasket thickness. Head gaskets for the 4AG run as low as 0.3mm, and quite commonly 0.5mm. This is far more of a restriction (think fluid flow properties) than the 0.4mm gallery gap from the head stud will ever be.

So lets get this perfectly clear. The problem ISNT with ARP head studs, its with a failure to build your engine properly! Your post should read:

Originally Posted by trd5k

The only factor that caused the cams to sieze was the rear locating dowel for cyl head was missing which caused the head to be moved slighty, but this was enough to block the hole completely.

what takai and andrew said. the cams get their oil through a dedicated gallery, not a stud hole... crank your engine with no head on and you'll soon see where it is. In fact if you're going through engines. do that test anyway

All cam journals are pressure fed as there is an oil gallery inside the cams. The head galleries are linked to the block gallery via the first head bolt hole on the exhaust side.
Anyone think I'll have a problem with oil feed to the head with a HKS restrictor, and ARP studs?

Last edited by jdm86gtz; 14th July 2011 at 05:22 AM.
Reason: Looked at head today